Search

This study explores a novel integration of electro-physicochemical technologies to generate energy and treat water from combined food waste (FW) and blackwater (FW-BW), with BW containing waste activated sludge with simulated flush water. The FW-BW substrate was gravity-separated and pretreated with hydrodynamic cavitation (HDC). Solids from gravity separation were used for energy generation via anaerobic digestion (AD) alone or integrated with microbial electrolysis cells (AD-MEC). HDC pretreatment had 51.6% more CH 4 production in 5 days (266 mL CH 4 /g VS) and 63% more in 30 days compared to AD without HDC. The CH 4 production after 5 days of digestion with HDC pretreatment (266 mL CH 4 /g VS) was similar to the amount produced without HDC over 30 days (263 mL CH 4 /g VS). Using MEC increased CH 4 production by 12.7% compared to AD-only. The liquids from gravity separation were treated with electrocoagulation (EC) at 15 V (90 min), which removed 96.2% of the chemical oxygen demand (COD) and 100% of the total suspended solids. The pilot scale design indicates that the AD-MEC and EC units would generate 1.4 times more energy than energy consumed through applying these novel technologies. These findings demonstration the applications of four technologies (HDC, AD, MEC, and EC) in an energy-efficient waste management approach, producing bioenergy and cleaner water for low-tier use, especially in areas lacking traditional waste treatment options. [Display omitted] • Novel technologies for energy and water treatment of food waste + blackwater. • HDC pretreatment had 51.6% more CH 4 production in 5 days than AD-only. • AD-MEC integration increased energy production by 12.7% compared AD-only. • Electrocoagulation at 15 V for 90 min removed 96.2% COD and 100% of solids. • A pilot scale AD-MEC design showed 1.4x more energy generated than energy input. [ABSTRACT FROM AUTHOR]

• Preservation of three inoculum sources via freeze-drying was evaluated. • All inoculum sources had viable CH 4 production with food waste after preservation. • The 10% skim milk cryoprotectant had 100% recovery of CH 4 after preservation. • Inoculum growth phase before preservation did not affect CH 4 recovery. • There was an increase in the lag phase after lyophilization from zero to eight days. A robust anaerobic digestion (AD) inoculum is key to a successful digestion process by providing the abundant bacteria needed for converting substrate to useable methane (CH 4). While transporting digester contents from one AD to another for digester startup has been the norm, transportation costs are high, and it is not feasible to transport wet inoculum to remote locations. In this study, the impact of preservation of AD inoculum via lyophilization was investigated for the purposes of digester startup and restabilization. The effect of lyophilizing inoculum on CH 4 production using food waste as the substrate was tested using biochemical methane potential (BMP) tests under the following conditions: (1) three inoculum sources, (2) two inoculum to substrate ratios (ISR), (3) two cryoprotectants, and (4) two inoculum growth phases. After lyophilization with skim milk, the three inocula produced 144–146 mL CH 4 /g volatile solids (VS) and 194–225 mL CH 4 /g VS at a 2:1 and 4:1 ISR, respectively, with 33–57% more CH 4 at the 4:1 ISR. Preservation with 10% skim milk exhibited complete recovery of CH 4 production, while 10% glycerol and 10% glycerol/skim milk mixture yielded 76% and 4% CH 4 recovery, respectively. Inoculum growth phase before preservation (mid-exponential or stationary growth phase) did not significantly affect CH 4 recovery. The study indicates that inoculum can be preserved via lyophilization using 10% skim milk as a cryoprotectant and reactivated for food waste digestion. The results provide a systematic quantification of the conditions needed to successfully preserve a mixed AD inoculum. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Metal nanoparticles (NPs) were added to anaerobic digestion (AD) of poultry litter. • Adding Ni NPs (12 mg/L) increased CH 4 production by 38.4% (368 mL CH 4 /g VS). • Fe, Co and Fe 3 O 4 NPs added individually also increased CH 4 with no effect on H 2 S. • Higher concentrations of NP mixtures greatly reduced H 2 S with no effect on CH 4. • A method for extraction of NPs from digestate for SEM detection was developed. Abstract The effects of metal nanoparticle (NP) addition during anaerobic digestion (AD) of poultry litter was tested using two sequential experiments: Exp. A) four NPs (Fe, Ni, Co, and Fe 3 O 4) at three concentrations; and Exp. B) NP combinations (Fe, Ni, and Co) at four concentrations. Scanning electronic microscopy (SEM) and elemental analysis were used to confirm NP inclusion after dispersion (before AD) and track nanoparticles post-AD, and new technique for NP extraction post-AD was developed. Before AD, NPs ranged from 30.0 to 80.9 nm for Fe, Ni, and Co, and 94.3 to 400 nm for Fe 3 O 4. Methane production increased with NPs addition compared to poultry litter-only, with the highest increases observed with NPs concentrations (in mg/L) of 12 Ni (38.4% increase), 5.4 Co (29.7% increase), 100 Fe (29.1% increase), and 15 Fe 3 O 4 (27.5% increase). Nanoparticle mixtures greatly decreased H 2 S production. The SEM post-AD detected Fe, Ni, and Fe 3 O 4 at concentrations ≥100 mg/L. [ABSTRACT FROM AUTHOR]

Three tubular anaerobic digestion (AD) systems were installed in Haiti to treat black water (toilet-based wastewater), including a three cell 36 m 3 clinic digester (CD), a two cell 2 m 3 hotel digester (HD), and a three-cell 3 m 3 farm digester (FD) for worker use. During digestion, total coliforms were reduced by 99.1%, E. coli by 98.5%, and chemical oxygen demand (COD) by 93.6%. Nutrients in the effluent averaged 99.4 mg/L NH 4 + and 10.6 mg/L PO 4 2− , producing an effective organic fertilizer. Average biogas production in CD was 108 L/d, with 65.4% CH 4 . Survey participants (n = 573) were willing to pay $0.10–0.30 per use for sanitation facilities. Seventy-two percent of the rural population surveyed in Cange, Haiti lacked access to improved sanitation due to financial constraints. The economic analysis calculated an investment cost for a shared toilet AD systems of $16–$47 (USD) per person based on daily use at design capacity. [ABSTRACT FROM AUTHOR]

There is a great need for decentralized anaerobic digestion (AD) that utilizes wastewater for energy generation. The biochemical methane potential (BMP) of Haitian latrine waste was determined and compared to other waste streams, such as grey water, septage, and dairy manure. Average methane (CH 4 ) production for the latrine waste (13.6 ml ml −1 substrate) was 23 times greater than septage (0.58 ml ml −1 substrate), and 151 times greater than grey water (0.09 ml ml −1 substrate), illustrating the larger potential when waste is source separated using the decentralized sanitation and reuse (DESAR) concept for more appropriate treatment of each waste stream. Using the BMP results, methane production based on various AD configurations was calculated, and compared with the full-scale field AD design. Methane potential from the BMP testing was calculated as 0.006–0.017 m 3 person −1 day −1 using the lowest and highest latrine BMP results, which was similar to the values from the full-scale system (0.011 m 3 person −1 day −1 ), illustrating the ability of BMPs to be used to predict biogas production from sanitation digesters in a smaller-scale setting. [ABSTRACT FROM AUTHOR]

Forage radish, a winter cover crop, was investigated as a co-substrate to increase biogas production from dairy manure-based anaerobic digestion. Batch digesters (300 cm 3 ) were operated under mesophilic conditions during two experiments (BMP1; BMP2). In BMP1, the effect of co-digesting radish and manure on CH 4 and H 2 S production was determined by increasing the mass fraction of fresh above-ground radish in the manure-based co-digestion mixture from 0 to 100%. Results showed that forage radish had 1.5-fold higher CH 4 potential than dairy manure on a volatile solids basis. While no synergistic effect on CH 4 production resulted from co-digestion, increasing the radish fraction in the co-digestion mixture significantly increased CH 4 production. Initial H 2 S production increased as the radish fraction increased, but the sulfur-containing compounds were rapidly utilized, resulting in all treatments having similar H 2 S concentrations (0.10–0.14%) and higher CH 4 content (48–70%) in the biogas over time. The 100% radish digester had the highest specific CH 4 yield (372 ± 12 L kg −1 VS). The co-digestion mixture containing 40% radish had a lower specific CH 4 yield (345 ± 2 L kg −1 VS) but also showed significantly less H 2 S production at start-up and high quality biogas (58% CH 4 ). Results from BMP2 showed that the radish harvest date (October versus December) did not significantly influence radish C:N mass ratios or CH 4 production during co-digestion with dairy manure. These results suggest that dairy farmers could utilize forage radish, a readily available substrate that does not compete with food supply, to increase CH 4 production of manure digesters in the fall/winter. [ABSTRACT FROM AUTHOR]

In anaerobic digestion, methane (CH 4 ) production decreases as temperature decreases, resulting in a lower CH 4 production at psychrophilic (≤25 °C) digestion temperatures. Previous studies at mesophilic temperatures (30–35 °C) have shown that manure separation and digesting only the liquid fraction could result in the reduction of digester volume without sacrificing CH 4 production. In this research, biochemical methane potential (BMP) tests were used to quantify CH 4 production of unseparated and separated manure at two psychrophilic temperatures: 14 and 24 °C. The results showed that CH 4 production decreased by approximately 70% when the temperature was decreased from 24 °C to 14 °C. Between days 20–216 at 24 °C, higher VS content of the unseparated manure resulted in significantly higher CH 4 production (29–40% more) compared to separated manure, on a volumetric basis, but at digestion times of ≤16 days, faster VS to CH 4 conversion rates in separated manure resulted in no significant differences in CH 4 production between the manure types. Similarly, at 14 °C, the higher VS content of the unseparated manure resulted in significantly higher CH 4 production (56–147% more) throughout most of 216-day experimental period, when normalized by volume. On a VS basis (mL CH 4 /g VS), the separated manure at 24 °C produced significantly more CH 4 than the other treatments. The study suggests that at 24 °C, there will be higher CH 4 production, per volume of manure added, from unseparated manure due to the higher VS content, but when operating at a shorter digestion time, the differences could be insignificant. [ABSTRACT FROM AUTHOR]

Pilot-scale digesters (850 L) were used to quantify CH 4 and H 2 S production when using forage radish cover crops as a co-digestion feedstock in dairy manure-based digesters. During two trials, triplicate mixed digesters were operated in batch mode with manure-only or radish + manure (27% and 13% radish by wet weight in Trial 1 and 2, respectively). Co-digestion increased CH 4 production by 11% and 39% in Trial 1 and 2, respectively. As H 2 S production rapidly declined in the radish + manure digesters, CH 4 production increased reaching high levels of CH 4 (⩾67%) in the biogas. Over time, radish co-digestion lowered the H 2 S concentration in the biogas (0.20%) beyond that of manure-only digestion (0.34–0.40%), although cumulative H 2 S production in the radish + manure digesters was higher than manure-only. Extrapolated to a farm-scale (200 cows) continuous mixed digester, co-digesting with radish could generate 3150 m 3 CH 4 /month, providing a farmer additional revenue up to $3125/month in electricity sales. [ABSTRACT FROM AUTHOR]

Highlights: [•] ATAs were conducted on four food processing wastes at 2%, 5%, 15% and 30% (by volume). [•] There were significant decreases in pH, with media addition, at each inclusion rate. [•] Above 5% inclusion, all four food processing wastes showed signs of toxicity. [•] Without co-digestion, CH4 production may be inhibited with food processing wastes. [Copyright &y& Elsevier]

Highlights: [•] Emergy analyses of digesters for human waste in Haiti and dairy manure in the US. [•] New emergy indices (EEI and AYR) were created for comparisons of analogous products. [•] Food and waste emergy analyses were conducted to determine waste emergy values. [•] Inputs from wastes accounted for more than 99% of the emergy in digesters. [•] When emergy waste values were zeroed, apparent sustainability improved. [ABSTRACT FROM AUTHOR]

Highlights: [•] BMPs were conducted on four food processing wastes co-digested with dairy manure. [•] Food waste addition was 3.2% by volume and 14.7–80.7% by volatile solids. [•] Methane increases of 67.0% (ice cream) to 2940% (chicken waste) were observed. [•] Due to manure co-digestion, there were no decreases in pH with no media added. [•] The study shows the large increases in CH4 possible with small volumetric additions. [ABSTRACT FROM AUTHOR]

Abstract: A life cycle assessment (LCA) approach was used to identify the processes and stages in organic waste composting that have the largest environmental impacts. The LCA included impacts associated with the collection of feedstock, production and distribution of compost, and its use as a replacement for peat for soil conditioning. The use phase of the compost product has not been included in previous LCA studies in the United States. Nine LCA impact categories were analyzed (global warming potential, ozone depletion, smog, acidification, eutrophication, carcinogens, non-carcinogens, respiratory effects, and ecotoxicity) using TRACI 2 methodology. The functional unit was defined as the collection, processing, transportation, and application of one tonne of compost that meets USEPA composting standards. The compost was produced at the Organics Material Processing and Education Center (OMPEC) at The Pennsylvania State University. The data used in the assessment was collected from seven composting windrows over thirteen consecutive months (December 2010–January 2012). Given the wide range of decomposition emission factors reported in the literature for methane (CH4), nitrous oxide (N2O) and ammonia (NH3), three emission scenarios were calculated: average, minimum, and maximum emission scenarios. Carbon dioxide (CO2) emissions from the compost were considered biogenic and not included in the assessment. For all scenarios, compost processing was the stage with the largest environmental impact, with decomposition emissions contributing the most to global warming potential, acidification and eutrophication impact categories under the average and maximum emissions scenarios. To account for the avoided environmental impacts of peat mining and transport, these values were subtracted from the composting life cycle. The avoided impacts from peat replacement were higher than the impacts from composting for all categories, illustrating that using compost instead of peat results in net environmental gains. This study highlights the importance of minimizing life cycle impacts associated with CH4, N2O and NH3 emissions during the decomposition process and the need for more consensus in the literature on emission values from composting processing. [Copyright &y& Elsevier]

Abstract: Anaerobic digestion (AD) is an economically viable manure treatment option for large dairies (>500 cows) in the U.S. However, roughly 90% of U.S. dairies have less than 200 cows, making this technology economically inaccessible to the vast majority of U.S. dairies. While there have been case studies of individual small dairies with anaerobic digesters, there are no comparative studies using cost data from these systems. The objectives of this study were to (1) determine the economic viability of small-scale U.S. digesters using cost data from nine existing 100 to 250-cow dairies and seven theoretical systems and (2) reevaluate the minimum size dairy farm needed for economically feasible AD in the U.S. Cash flow analysis results showed that total capital costs, capital costs per cow, and net costs per cow generally decreased with increasing herd size in existing systems. Among existing revenue streams, use of digested solids for bedding generated the highest revenue ($100cow−1 year−1), followed by biogas use for heating and/or electrical generation ($47 to $70cow−1 year−1) and CO2 credits ($7cow−1 year−1). No system had a positive cash flow under the assumed conditions (8% discount rate, 20-year term). However, six of the 16 systems had positive cash flows when 50% cost sharing was included in the analysis. Our results suggest that, with cost sharing, economically viable AD systems are possible on 250-cow dairies. Additional revenue streams, such as tipping fees for food waste, may reduce the minimum size to 100-cow dairies. [Copyright &y& Elsevier]

Abstract: An emergy analysis was performed to assess the relative sustainability and environmental impact of small-scale energy production using Taiwanese model plug-flow anaerobic digesters to treat livestock manure in Costa Rica. Emergy analysis quantifies all inputs to a system by converting them to solar energy equivalents, thus allowing for direct comparison of the diverse inputs of renewable energies, human labor and economic goods needed to construct and maintain anaerobic digestion systems. The digesters were located on the campus of EARTH University, Costa Rica, and the biogas was utilized to power a 40kW generator that supplies electricity for farm operations. Separate emergy analyses were performed for the biogas production and the combination of biogas production and generation of electricity. Manure was the largest input in both analyses, accounting for 85.3% of the annual emergy input for biogas production and 66.9% for electricity generation from the biogas. The fraction of emergy inputs from renewable sources (ΦR) was 66% for biogas production and 52% for electricity generation from the biogas. The transformities of biogas and electricity generation from the biogas were 5.23E+04sej/J and 1.01E+06sej/J respectively. The emergy yield ratios (EYR) were 2.93 for biogas production and 2.07 for electricity generation indicating that these digesters efficiently match purchased resources and renewable energies to produce energy from livestock manure. The generation of electricity from the biogas resulted in a decrease in the emergy sustainability index (ESI) from 5.67 to 2.22 and an increase in the environmental loading ratio (ELR) from 0.52 to 0.93. Using a generator to convert the biogas to electricity does decrease the sustainability of the system, largely due to the high emergy value associated with the electrical generation equipment and machinery, but these results demonstrate that the production of biogas and the generation of electricity from Taiwanese model digesters in Costa Rica are environmentally sustainable processes that result in the production of energy that is largely dependent on renewable and recycled energies. [Copyright &y& Elsevier]

Abstract: A nine-month co-digestion investigation was conducted in Costa Rica to optimize animal wastewater treatment, renewable energy production, and fertilizer creation using 12 Taiwanese-model, plug-flow digesters (250 L each) constructed of tubular polyethylene and PVC piping, operating without mechanical or heating components. The experiment tested three replications of four treatment groups: the control (T0), which contained only swine manure, and T2.5, T5, and T10, which contained 2.5%, 5%, and 10% used cooking grease (by volume) combined with swine manure. T2.5 had the greatest methane production (45 L d−1), a 124% increase from the control. No adverse effects were observed from co-digesting 2.5% grease in terms of organic matter removal, pathogen reduction, grease removal, and pH. Chemical oxygen demand (COD) was reduced 94.7% to 1.96 g L−1, fecal coliforms and Escherichia coli were reduced 99.2 and 97.1%, respectively, and grease removal was 99.9%. The average effluent pH (7.05) and alkalinity in T2.5 was within the optimal range for methanogens and increased significantly during the nine-month experiment, likely due to adaptation of the methanogenic organisms to the influent grease concentrations. Total nitrogen concentration decreased 34.0%, and NH4-N increased 97.1% during digestion in T2.5, with no significant differences between T2.5 and T0. There was less phosphorus reduction with co-digestion, with 181 mg g−1 of total phosphorus (TP) in T2.5 and only 90.6 mg g−1 of TP in T0, resulting in lower N:P ratios in the grease treatment groups due to the greater concentration of phosphorus in the effluent. [Copyright &y& Elsevier]

Abstract: A co-digestion investigation was conducted using small-scale digesters in Costa Rica to optimize their ability to treat animal wastewater and produce renewable energy. Increases in methane production were quantified when swine manure was co-digested with used cooking grease in plug-flow digesters that operated at ambient temperate without mixing. The co-digestion experiments were conducted on 12 field-scale digesters (250L each) using three replications of four treatment groups: the control (T0), which contained only swine manure and no waste oil, and T2.5, T5, and T10, which contained 2.5%, 5%, and 10% used cooking grease (by volume) combined with swine manure. The T2.5 treatment had the greatest methane (CH4) production (45L/day), a 124% increase from the control, with a total biogas production of 67.3L/day and 66.9% CH4 in the produced biogas. Increasing the grease concentration beyond T2.5 produced biogas with a lower percentage of CH4, and thus, did not result in any additional benefits. A batch study showed that methane production could be sustained for three months in digesters that co-digested swine manure and used cooking grease without daily inputs. The investigation proved that adding small amounts of grease to the influent is a simple way to double energy production without affecting other digester benefits. [Copyright &y& Elsevier]

Abstract: Methane production, electricity production, and wastewater transformations were quantified for a digestion system that combines biogas from a swine digester and dairy digester in Costa Rica. The low-cost, plug-flow digesters were not heated and were operated in the lower portion of the mesophilic range (25–27°C). The dairy digester produced 27.5m3/day of biogas with 62.6% methane and reduced organic matter (COD) by 86%. The swine digester produced 6.0m3/day of biogas with 76.4% methane and reduced COD by 92%. Combining biogas from a swine and dairy digester, increased electricity production due to the higher biogas production rate of the dairy farm and the higher quality biogas obtained from the swine farm. The farm’s 2-h peak electricity demand (12.9kW/day) was 81.8% met. The electricity was produced using manure equivalent to the quantity excreted by 5 dairy cows and 40 pigs remaining in corrals 100% of the time. The $21,000 capital cost of the digester project will be recovered in 10.1 years through electricity savings and reductions in wastewater fines. If the generator were more appropriately sized for the farm, the capital recovery time would have been 7.6 years. [Copyright &y& Elsevier]

Seven low-cost digesters in Costa Rica were studied to determine the potential of these systems to treat animal wastewater and produce renewable energy. The effluent water has a significantly lower oxygen demand (COD decreased from 2968mg/L to 472mg/L) and higher dissolved nutrient concentration (NH4-N increased by 78.3% to 82.2mg/L) than the influent water, which increases the usefulness of the effluent as an organic fertilizer and decreases its organic loading on surface waters. On average, methane constituted 66% of the produced biogas, which is consistent with industrial digesters. Through principle component analysis, COD, turbidity, NH4-N, TKN, and pH were determined to be the most useful parameters to characterize wastewater. The results suggest that the systems have the ability to withstand fluctuations in the influent water quality. This study revealed that small-scale agricultural digesters can produce methane at concentrations useful for cooking, while improving the quality of the livestock wastewater. [Copyright &y& Elsevier]

Abstract: Ecological Treatment Systems (ETS) are composed of a series of anaerobic and aerobic reactors, clarifiers, and wetlands, and have been used for the removal of nutrients from municipal and industrial wastewaters. The design of ETS enhances nutrient removal by providing both aerobic and anaerobic environments and steep gradients between the two environments. The ability of an ETS to treat wastewater from a dairy farm was investigated with a 20-week study in Columbus, OH, USA. The Waterman Ecological Treatment System (WETS) had four replicate treatment lines. Together, the four lines treated 1310L/day of diluted wastewater from a dairy facility with over 99% removal of ammonium-nitrogen (NH4-N) and carbonaceous biochemical oxygen demand (CBOD), and 79% removal of orthophosphate (PO4-P). The average influent/effluent concentrations of NH4-N, CBOD, and PO4-P were 52.1/0.07mg/L, 517/5.2mgO2/L, and 21.0/4.4mg/L, respectively. Nitrate+nitrite (NO x -N) was produced and removed within the system, and had an average effluent concentration of 0.53mg/L. The multiple anaerobic–aerobic interfaces in the WETS design enhanced biological removal of nitrogen and phosphorus. NH4-N, CBOD, and NO x -N were consistently removed throughout the 20-week study, but PO4-P removal efficiency decreased over time in one of the four treatment lines. [Copyright &y& Elsevier]

Hydrogen sulfide (H 2 S) in biogas is produced during anaerobic digestion of organic wastes and can lead to corrosion of generators used for energy production. Recently, there has been interest in utilizing biochar as a substitute for activated carbon (AC) to adsorb and remove H 2 S from biogas. This study was the first to test iron (Fe)-impregnation of biochar to increase H 2 S removal from biogas using a biogas scrubbing column. Two biochar substrates, corn stover biochar (CSB) and maple wood biochar (MB), with and without Fe-impregnation were evaluated for H 2 S adsorption from biogas. The H 2 S adsorption capacity was quantified using dynamic breakthrough experiments. Iron-impregnated maple biochar (MB-Fe) had the highest H 2 S saturation adsorption capacity (23.9 mg H 2 S g−1 biochar), which was 3.9 times higher than the unmodified MB (6.1 mg H 2 S g−1 biochar). The Fe-impregnated corn stover biochar (CSB-Fe) saturation H 2 S sorption capacity (8.2 mg H 2 S g−1 biochar) was 2.5 times higher than the unmodified CSB (3.3 mg H 2 S g−1 biochar). The presence of iron oxide (Fe 3 O 4) was observed through X-ray diffraction and scanning electron microscopy in the Fe-impregnated biochar substrates, with ferrous sulfate (FeSO 4) as one of the end products in the saturated biochar surface and elemental sulfur in the pores. The study showed how Fe-impregnation can result in a multifold increase in H 2 S adsorption from biogas compared to unmodified biochar. ga1 • Iron-impregnation resulted in up to 3.9 times increase in H 2 S adsorption capacity. • Adsorption capacity of unmodified MB was 2.5 times higher than CSB. • H 2 S adsorption capacity of unmodified biochar was comparable to activated carbon. • Iron impregnation increased the Fe content of biochar from 1100 ppm to 29,700 ppm. • Fe 3 O 4 in the impregnated biochar was converted to FeSO 4 after reaction with H 2 S. [ABSTRACT FROM AUTHOR]

• Unmodified biochar added to a digester resulted in 90.5% H 2 S removal efficiency. • The biochar particle size did not significantly affect the H 2 S removal efficiency. • Iron-impregnated biochar resulted in complete removal of H 2 S from the biogas. • Activated carbon was not effective when used as an in-situ desulfurization agent. • Biochar addition did not significantly affect the methane yield during digestion. Corn stover biochar (CSB) and maple biochar (MB) were added into anaerobic digesters and evaluated for hydrogen sulfide (H 2 S) reductions. This was the first study to show Fe-impregnated biochar can eliminate H 2 S production. The novel study evaluated biochar addition on H 2 S reduction and nutrient concentrations using three experiments to test the effect of: 1) biochar concentration, 2) biochar particle size, and 3) Fe-impregnated biochar using triplicate lab-scale reactors. At the highest biochar dose (1.82 g biochar/g manure TS), H 2 S production was 90.5% less than the control treatment (351 mL H 2 S/kg VS). Biochar particle size did not significantly affect H 2 S concentration. The Fe-impregnated biochar (0.5 g biochar/g manure TS) reactors had no H 2 S detected in the CSB-Fe system. Methane (CH 4) in the biochar and control treatments were not significantly different in all three experiments. The results show that biochar added to digesters can significantly reduce H 2 S production without affecting CH 4 production. [ABSTRACT FROM AUTHOR]

Temperature is a critical factor affecting anaerobic digestion because it influences both system heating requirements and methane production. Temperatures of 35–37 °C are typically suggested for manure digestion. In temperate climates, digesters require a considerable amount of additional heat energy to maintain temperatures at these levels. In this study, the effects of lower digestion temperatures (22 and 28 °C), on the methane production from dairy digesters were evaluated and compared with 35 °C using duplicate replicates of field-scale (FS) digesters with a 17-day hydraulic retention time. After acclimation, the FS digesters were operated for 12 weeks using solids-separated manure at an organic loading rate (OLR) of 1.4 kg VS m −3 d −1 and then for 8 weeks using separated manure amended with manure solids at an OLR of 2.6 kg VS m −3 d −1 . Methane production values of the FS digesters at 22 and 28 °C were about 70% and 87%, respectively, of the values from FS digesters at 35 °C. The results suggest that anaerobic digesters treating dairy manure at 28 °C were nearly as efficient as digesters operated at 35 °C, with 70% of total methane achievable at 22 °C. These results are relevant to small farms interested in anaerobic digestion for methane reduction without heat recovery from generators or for methane recovery from covered lagoon digesters. [ABSTRACT FROM AUTHOR]

• Conventional volatile fatty acid recovery from waste is energy prohibitive. • Hydrophobic deep eutectic solvents enable low-energy volatile fatty acid adsorption. • Omniphobic membrane selectively allows undissociated volatile fatty acids to pass. • Volatile fatty acid recovery will revolutionize the conventional anaerobic digestion. Volatile fatty acids (VFAs) derived from arrested anaerobic digestion (AD) can be recovered as a valuable commodity for value-added synthesis. However, separating VFAs from digestate with complex constituents and a high-water content is an energy-prohibitive process. This study developed an innovative technology to overcome this barrier by integrating deep eutectic solvents (DESs) with an omniphobic membrane into a membrane contactor for efficient extraction of anhydrous VFAs with low energy consumption. A kinetic model was developed to elucidate the mechanistic differences between this novel omniphobic membrane-enabled DES extraction and the previous hydrophobic membrane-enabled NaOH extraction. Experimental results and mechanistic modeling suggested that VFA extraction by the DES is a reversible adsorption process facilitating subsequent VFA separation via anhydrous distillation. High vapor pressure of shorter-chain VFAs and low Nernst distribution coefficients of longer-chain VFAs contributed to DES-driven extraction, which could enable continuous and in-situ recovery and conversion of VFAs from AD streams. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • FNA pretreatment can significantly improve the solubilization of organic waste. • pH change within the system can adversely impact the FNA pretreatment performance. • Effective FNA concentration may decrease due to NO 2 – consumption by denitrifiers. • FNA-pretreated organic waste does not always show a higher biogas production in AD. • FNA at 1.0–5.2 mg FNA-N/L effectively controlled H 2 S-odor in the organic wastes. This work investigated the effectiveness of free nitrous acid (FNA) in enhancing organic waste solubilization to improve biogas production in anaerobic digestion (AD). The results indicated that FNA pretreatment can enhance soluble organic content and control H 2 S odor in tested organic wastes, including food waste, sewage sludge, and their combination. However, a significant decrease (>50 %) in FNA concentration was found in the reactors, possibly due to denitrifier-driven NO 2 – consumption. Biochemical methane potential (BMP) tests showed a 25 ± 8 % enhancement in CH 4 production in the reactors fed with mixed substrate pretreated with 2.9 mg FNA-N/L. However, the presence of NO 2 – (325.6–2368.0 mg N/L) in some BMP reactors, due to carryover from FNA pretreatment, adversely affected CH 4 production (>55 %) and prolonged lag time (>4.2 times). These findings are valuable for researchers and practitioners in waste management, offering insights for implementing FNA pretreatment to enhance the biodegradability of organic wastes in AD. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conductive NPs potential to improve AD performance was critically discussed. • Impact of different NPs and sizes on AD biogas quantity and quality are elucidated. • The interactions of AD microorganisms and DIET with the aid of NPs were reviewed. • The role of NPs in biochemical pathways direction and metabolites utilization are covered. Anaerobic digestion (AD) is a biochemical process that converts waste organic matter into energy-rich biogas with methane as the main component. Addition of electric electro-conductive, such as that nanoparticles (NP), has been shown to improve biogas generation. Interspecies electron transfer and direct interspecies electron transfer (DIET) using conductive materials is one of the mechanisms responsible for observed increases in CH 4. This article discusses the effect of the type and size of electro-conductive NPs on improving microbial degradation within AD systems, as well as the effect of electro-conductive NPs on microbial community shifts and syntrophic metabolism. Limitations and future perspectives of using NPs in an AD system is also discussed. [ABSTRACT FROM AUTHOR]

• Tracked nanoparticle (NP) use, degradation, and uptake in an AD-hydroponics system. • NP use increased CH 4 production by 23.7% during anaerobic digestion (AD). • NP addition temporarily ceased H 2 S production, with an average reduction of 56.3%. • The AD treated with NPs had 1,160–19,400% higher NP concentrations in the effluent. • Harvested lettuce had 21.0–1,920% more NP uptake, yet, well below toxic thresholds. Nanoparticle (NP) use can increase biological activity and adversely impact the environment. This study was the first to quantify biogas increases with NP mixtures during continuous anaerobic digestion (AD) of poultry litter and NP uptake in crops through tracking: 1) CH 4 and H 2 S production from a NP mixture (Fe, Ni, and Co) in 30 L continuous digester (AD1) for 278 days compared to a control digester (AD2) without NP addition, 2) NP degradation during digestion, 3) using AD effluent with and without NP addition as a fertilizer, and 4) plant uptake of NPs. With NP inclusion, CH 4 production increased by 23.7%, and H 2 S was reduced by 56.3%. The AD1 effluent had 1,160–19,400% higher NP concentrations and the lettuce biomass had 21.0–1,920% more NPs than lettuce fertilized with the AD2 effluent. This study showed that the effects of NPs remaining in the AD effluent must be considered. [ABSTRACT FROM AUTHOR]

This study determined the effect of incorporating a microbial electrolysis cell (MEC) with an anaerobic digester (AD) in a single chamber. The study evaluated three treatments: a combined AD-MEC operated for 23 days (AD-MEC-23); a combined AD-MEC operated with the MEC running for 5 days followed by no MEC for the subsequent 18 days (AD-MEC-5); and an AD operated for 23 days (AD-only). Food waste was the digestion substrate at an inoculum to substrate ratio of 1:1 (VS basis). Cumulative methane and hydrogen during the batch test in AD-MEC-23 (9.4 L CH4 , 3.39 L H2 , 2.8 L CO2 ) was higher than AD-MEC-5 (7.6 L CH4 , 2.2 L H2 , 4.6 L CO2 ), and AD-only (7.4 L CH4 , 0.2 L H2 , 5.8 L CO2 ). The results also showed that using the MEC continuously inside the digester (AD-MEC treatment) reduced CO 2 concentration to approximately 4% at the end of the experimental period, thereby, increasing the useful gases (CH 4 and H 2 ) concentrations to a maximum of 95.8%, with an average of 71.9% CH 4 , 17.4% H 2 and 10.7% CO 2 over the 23-day digestion period in the AD-MEC-23 reactor. Additionally, the COD removal in AD-MEC-23 was 12% higher than AD-only. The volumetric current was 108.7 A/m 3 based on MEC volume and 17.3 A/m 3 based on total AD-MEC volume, while the current density was 1.35 A/m 2 (cathode surface area). The total energy produced from the AD-MEC-23 (414 kJ) was higher than AD-MEC-5 (325 kJ) and AD-only (295 kJ), with an increase of energy production of over 400% output energy compared to the input energy to power the MEC. The results showed that the novel MEC design incorporated into an AD reactor increased the biogas quality, overall energy production, and waste treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Industrial waste is with 35.2% most common substrate used in two-stage systems. • High methane contents of 85% can be reached with two-stage anaerobic digestion. • The pH in the first stage influences process stability and performance parameters. • With a higher process efficiency, the two-stage approach saves material costs. • Biomethane by two-stage high-pressure anaerobic digestion substitutes fossil fuels. Two-stage anaerobic digestion (TSAD) systems have been studied on a laboratory scale for about 50 years. However, they have not yet reached industrial scale despite their potential for future energy systems. This review provides an analysis of the TSAD technology, including the influence of process parameters on biomass conversion rates. The most common substrate (35.2% of the 38 selected studies) used in the analysed data was in the category of rapidly hydrolysable industrial waste with an average dry matter content of 7.24%. The highest methane content of 85% was reached when digesting food waste in a combination of two mesophilic continuously stirred tank reactors with an acidic (pH 5.5) first stage and alkaline (pH 7) second stage. Therefore, the review shows the limitations of the TSAD technology, future research directions, and the effect of integration of TSAD systems into the current strategy to reduce greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Abstract: The presence of SXT/R391-related integrating conjugative elements (ICEs) in Vibrio cholerae O1 and non-O1/non-O139 isolated from clinical and environmental samples in Haiti in 2010 was studied. The main finding of this work was the identification of the novel ICEVchHai2 among closely related V. cholerae non-O1/non-O139 clinical strains. The mosaic structure of this element confirms the role of ICEs as efficient recombination systems whereby new genetic material can be acquired and exchanged, according V. cholerae strains new accessory functions. [Copyright &y& Elsevier]

Combustion can concentrate phosphorus (P) from poultry litter into an ash product that is easier to transport for land application. This was the first life cycle assessment (LCA) study to investigate the efficacy and sustainability of a fluidized bed combustion (FBC) system using poultry litter to heat poultry houses and produce electricity, in the United States, to replace liquid propane gas (LPG) and natural gas (NG) use. The 'Baseline scenario' used results from a 16-month FBC monitoring study, and an 'Improved scenario' based on an increased biomass feed rate (0.246 tons/h), increased run-time (6720 h/y), and net positive electricity production. In the Baseline scenario, climate change potential was 32% and 44% lower than use of LPG and NG, respectively, for poultry house heating, but the low electricity production from the FBC system resulted in net electricity import and lower sustainability compared to LPG use in 12 of the 18 impact categories. The Improved scenario had 48–98% less environmental impacts than the Baseline scenario in the 18 categories. The sensitivity analysis showed that a 10% change in the electricity input for FBC operation resulted in the highest average change (4.8%) in the 18 impact categories, indicating the necessity of a net positive electrical energy output from the FBC unit for increased sustainability. The results also highlighted the impact of the replacement heating fuel type, as replacing NG through poultry litter combustion had a greater impact than replacement of LPG. • Combustion of poultry litter can be a sustainable form of manure management. • Climate change potential was 32% and 44% lower than using LPG and NG for heating. • The avoided use of LPG offset the impacts in 6 out of 18 categories analyzed. • Electricity input to the FBC system had the highest overall environmental impact. • If the FBC operated with a net electricity export, impacts decreased by >48%. [ABSTRACT FROM AUTHOR]

Algal turf scrubbers (ATS) and anaerobic digesters (AD), when combined, remove nutrients from eutrophic water while producing renewable energy through biogas production. Algal biomass was produced from an ATS system that used tipping buckets to introduce riverine water in pulses onto a flow-way with a mesh screen installed to facilitate algal attachment. This study was the first to determine methane (CH 4) production from AD of a micro- and macro-algae polyculture, harvested from an ATS, using lab-scale reactors under batch and semi-continuous feeding regimes. The lab-scale study was followed by a pilot-scale (7 m3) ATS-AD study, the largest scale study of biogas production from ATS-derived algae. Batch digestion of 'wet' algae (93% moisture) produced 158 ± 13 L CH 4 /kg VS, which was higher than algae with a lower moisture content (≤62% moisture). Continuing use of 'wet' algae as the substrate, the 2 L semi-continuously-fed lab system yielded a maximum CH 4 production value of 144 ± 7 L CH 4 /kg VS, with 60%–62% CH 4 in the biogas. The 7 m3 pilot-scale system produced 107 ± 15 L CH 4 /kg VS, with 66.4% CH 4 in the biogas. Scale-up calculations showed that a 1 ha ATS system could capture 8.73 kg N, 1.18 kg P, and 52.5 kg C/ha-d, with the resulting algae being used in AD to produce biogas for direct heating (2.8*108 J) or to power a 1.13 kW generator. While the total energy output from the 1 ha ATS-AD system is relatively low, energy production from the AD system is a supplemental benefit to an ATS system that captures nutrients from eutrophic water. This ATS-AD system could contribute to the overall Chesapeake Bay cleanup, especially in nutrient hot-spots, like the Baltimore Harbor, where high nutrient concentrations support high algal productivity, which would provide substrate for on-site energy production from AD. Unlabelled Image • Biomass from algal turf scrubber (ATS) that removed nutrients from eutrophic waters. • Methane production from ATS biomass was 158 L CH 4 /kg VS with 'wet' algae (TS = 7%). • Max CH 4 production in semi-continuous reactors was 144 L CH 4 /kg VS with 20-day HRT. • 7 m3 pilot-scale digester produced 107 L CH 4 /kg VS, with 66.4% CH 4 in the biogas. • Scale-up to 1 ha would remove 8.7 kg N/d, 1.18 kg P/day and produce 1.13 kW of power. [ABSTRACT FROM AUTHOR]